I would think it would be fair to offer the vehicle for maybe 5k.
And dont forget to add the OBO.
I only wish you had some smallers pics so I can see the car in full view.
I am currently selling my 75 for 4500 OBO. But then again, mine isnt full of rust.... however it is in need of an overhaul. It still has the original inline 6 250hp motor.
So.... I think you are really the only one who can decide the value of your vehicle.
But first try researching and comparing what others had sold the same car for, that is also in the same near condition.
Good Luck to ya!